1. Field of the Invention
This invention relates to a magnetic sensor utilizing magnetoresistance, a magnetic recording.cndot.reproducing head, and a magnetic recording.cndot.reproducing apparatus using the magnetic sensor.
2. Description of the Related Art
As a means for reading out a signal recorded in a magnetic recording medium, the method which comprises causing a reading magnetic head as a magnetic sensor possessed of a coil to be moved relative to the magnetic recording medium and detecting the voltage which is induced in the coil by the electromagnetic induction generated in consequence of the relative motion has been widely known heretofore.
Meanwhile, the magnetoresistance (hereinafter referred to as "MR") head which utilizes the phenomenon that the electrical resistance of a certain kind of ferromagnetic body is varied proportionately to the intensity of an external magnetic field has been finding recognition as a high-sensitivity head adapted for the detection of a signal magnetic field of the magnetic recording medium. In recent years, magnetic recording media have been trending toward smaller sizes and larger capacities and the relative speeds between reading magnetic heads and magnetic recording media have been on the decrease and, accordingly, expectations for an MR head which is capable of reading out a large output in spite of a small relative speed have been mounting.
When an MR head is actually used as a magnetic reproducing head, it is generally necessary that two kinds of bias magnetic field be applied to the MR element. One of the two kinds is a magnetic field designated as that of lateral bias which is applied substantially perpendicularly to the sense current for detecting the variation of the resistance of the MR element. This is the bias magnetic field which is intended to set the point of operation of the MR element in a linear region in which the magnitude of an external signal is proportionate to that of a detecting signal. As concrete examples of the method for applying the lateral bias, a self bias method which comprises parallelly opposing an MR film and a soft magnetic film through the medium of a thin nonmagnetic film and utilizing a magnetic field generated by a sense current as the lateral bias and a shunt bias method are generally cited. The other kind of bias magnetic field to be applied to the MR element is a magnetic field designated as that of longitudinal bias which is applied substantially parallelly to the sense current of the MR element. This is the bias magnetic field which is intended to repress the occurrence of Barkhausen noise due to the multidomain property by imparting a single domain property to the MR film which is a ferromagnetic film.
Numerous reports have been heretofore published regarding the method for applying such longitudinal bias as described above. U.S. Pat. No. 4,663,685, for example, discloses a technique for applying uniform longitudinal bias to the MR film by the exchange coupling of an antiferromagnetic film and a ferromagnetic film. FIG. 18 is a perspective view illustrating one example of the construction of an MR element having longitudinal bias applied to an MR film by the use of an antiferromagnetic film. In the MR element of this construction, antiferromagnetic films 3 and 3 are formed as interposed between the opposite end parts in the direction of track width of the MR film destined to serve as a signal magnetic field detecting film 1 and terminals 2 and 2 for supplying a sense current, for example, as shown in the diagram. In FIG. 18, the MR film is depicted as formed on a substrate 6 so as to be opposed to a soft magnetic film 5 through the medium of a nonmagnetic film 4. The magnetic field generated by the sense current is applied as lateral bias to the MR film.
The construction of the element shown in FIG. 18, however, entails the problem of encountering difficulty in repressing the exchange coupling force with the antiferromagnetic films 3 and 3 to the extent of preventing the magnetizations of the opposite end parts of the MR film destined to form the signal magnetic field detecting film 2 from being fixed and consequently suffered to impair the soft magnetic property. Though the magnetizations of the opposite end parts of the MR film are not completely fixed, at least the soft magnetic property of the MR film differs between the opposite end parts and the central part thereof. When the MR film is used for a magnetic reproducing head, therefore, it becomes difficult to attain accurate regulation of the track width. Further, since the .gamma.-FeMn alloy generally used for the antiferromagnetic film 3 is deficient in resistance to corrosion, the antiferromagnetic film 3 necessitates provision therefor a protective film, for example. The process used for the production of this film, therefore, is complicated.
U.S. Pat. No. 3,840,898 discloses an MR element which applies longitudinal bias to an MR film by the magnetostatic coupling between ferromagnetic films. FIG. 19 is a perspective view illustrating an example of the construction of this MR element. In the MR element, the MR film destined to serve as a signal magnetic field detecting film 1 is opposed to a hard magnetic film 8 through the medium of a thin nonmagnetic film 7 on a substrate 6 as shown in the diagram. Terminals 2 and 2 for supplying a sense current are formed on the opposite end parts in the direction of track width of the hard magnetic film 8. In this construction, a magnetization M.sub.1 having a component perpendicular to the film surface is generated within the hard magnetic film 8 because hexagonal c axis, for example, of the hard magnetic film 8 is almost inplane oriented but there exists perpendicular component to the film surface. As a result, not only a bias magnetic field M.sub.2 from the opposite end parts in the direction of track width of the hard magnetic film 8 but also a leak magnetic field M.sub.3 near the center of the hard magnetic film 8 is applied to the MR film via the nonmagnetic film 7. As a result, the soft magnetic property of the MR film destined to serve as the signal magnetic field detecting film 1 is impaired and the sensitivity of the MR element is consequently degraded.
Since the soft magnetic property of a MR film is impaired when the longitudinal bias is applied near the center of the MR film as described above, it has been proposed to obtain a construction for applying longitudinal bias by forming a hard magnetic film exclusively near the opposite end parts in the direction of track width of a MR film. Particularly, JP-A-05-89,435, JP-A-03-108,112, etc. disclose attempts to simplify the process for production of an MR element by fixing the magnetic moment of the opposite end parts in the direction of track width of an MR film and a soft magnetic film for application of lateral bias thereby forming hard magnetic films for application of longitudinal bias. FIG. 20 and FIG. 21 are perspective views which show examples of the constructions of MR elements disclosed in JP-A-05-89,435 and JP-A-03-108,112.
The MR film shown in FIG. 20 is produced by forming an MR film on a substrate 6 and then incorporating a desired impurity component in the opposite end parts of the MR film thereby fixing the magnetic moment of the opposite end parts exclusively. The fixed regions function as hard magnetic films 3 and 3 and the part intervening therebetween functions as a signal magnetic field detecting film 1. The magnetic fields from the fixed regions functioning as the hard magnetic films 3 and 3 are applied as longitudinal bias to the MR film serving as the signal magnetic field detecting film 1. Terminals 2 and 2 for supplying a sense current are superposed on the hard magnetic films 3 and 3. The MR element shown in FIG. 21 is obtained by sequentially superposing an MR film destined to serve as a signal magnetic field detecting film 1, a nonmagnetic film 9, and a soft magnetic amorphous film in the order mentioned on a substrate 6 and crystallizing the opposite end parts in the direction of track width of the soft magnetic amorphous film by exposure to a laser beam. Then, the central part of the soft magnetic amorphous film is made to function as a soft magnetic film 10 for application of lateral bias and the crystallized opposite end parts are made to function as hard magnetic films 3 and 3 for application of longitudinal bias. Terminals for supplying a sense current are formed on the hard magnetic films 3 and 3.
In the case of the MR element shown in FIG. 20, however, the magnetizations near the opposite end parts of the MR film as the signal magnetic field detecting film 1 are still liable to be fixed. The MR element, therefore, has the problem that the whole area of the MR film in the direction of track width cannot be used as a signal magnetic field sensing part and the track width cannot be accurately regulated. Further, since this MR element must use for the MR film a ferromagnetic substance which is capable of being fixed by incorporation of an impurity component and, therefore, entrains a heavy restriction on the selection of material, it is not allowed to use for the MR film a ferromagnetic substance exhibiting a highly satisfactory soft magnetic property and possessing an ample ratio of variation of resistance. Then, in the MR element shown in FIG. 21, magnetic poles formed in the end parts of the hard magnetic films 3 and 3 are utilized for applying to the opposite end parts in the direction of track width of the MR film as the signal magnetic field detecting film 1 a magnetic field of a direction opposite to the direction of the magnetic field applied to the central part. The MR element, therefore, incurs difficulty in imparting a single domain property to the MR film and has no ability to repress the Barkhausen noise of the MR element sufficiently. The magnetic poles formed in the end parts of the hard magnetic films 3 and 3 constitute themselves a factor for obscuring the track width of the signal magnetic field detecting film 1.
JP-A-04-358,310 discloses an MR element provided with a spin valve film exhibiting giant magnetoresistance and adapted to apply longitudinal bias to a ferromagnetic film destined to serve as a signal magnetic field detecting film by the use of a hard magnetic film. FIG. 22 is a perspective view showing an example of the construction of this MR element. As shown in the diagram, in this MR element, a ferromagnetic film destined to serve as a signal magnetic field detecting film 1 is formed on a substrate 6, a nonmagnetic film 11 and a ferromagnetic film 12 are superposed sequentially in the order mentioned in the central part in the direction of track width of the ferromagnetic film, and the magnetization of the ferromagnetic film 12 is fixed in a direction substantially perpendicular to the direction of track width to form a spin valve film 1. On the opposite end parts in the direction of track width of the ferromagnetic film destined to serve as the signal magnetic field detecting film 1, hard magnetic films 33 for the application of longitudinal bias and terminals 2 and 2 for the supply of a sense current are formed.
In the MR element described above, however, the whole area in the direction of track width of the signal magnetic field detecting film 1 is not allowed to form a signal magnetic field sensing part because the magnetization of the ferromagnetic film destined to serve as the signal magnetic field detecting film 1 tends to be fixed directly under and near the edge of the hard magnetic films 3 and 3. As a result, it has the problem of its inability to regulate accurately the track width. Further, the regulation of the direction of magnetization of the ferromagnetic film 12 is not easily attained because the magnetic field from the hard magnetic films 3 and 3 is applied also to the ferromagnetic film 12.
When the magnetic sensor provided with the signal magnetic field detecting film exhibiting magnetoresistance as described above is used as a magnetic reproducing head, for example, the MR element using the conventional method for the application of longitudinal bias is at a disadvantage in terms of construction of a device as in incurring difficulty in accurately regulating the track width and in entailing degradation of sensitivity. This problem gains in prominence when the width of the track is decreased for the purpose of exalting record density.
Further, such obscurity of the track width of the magnetic reproducing head as mentioned above also forms a cause for the following problem when the magnetic reproducing head is used as a magnetic head in which recording head is integrated on a reproducing head. Specifically, as a magnetic head which uses a shield type MR head as a reproducing head, the construction shown in FIG. 23 is generally adopted, for example. As shown in the diagram, an MR film designed to serve as a signal magnetic field detecting film 1 and terminals for the supply of a sense current are formed on a lower shield layer 14 through the medium of a magnetic gap 15. On the MR film and the terminals 2 and 2, an upper shield layer 17 is formed through the medium of a magnetic gap 16. These components jointly form a reproducing head utilizing magnetoresistance. Since the upper shield layer 17 concurrently serves as a lower magnetic pole layer for the recording head, an upper magnetic pole layer 19 is formed thereon through the medium of a recording gap 18.
Then, in the conventional magnetic head, since the reproducing head does not allow accurate regulation of the track width thereof, the track width of the recording head is generally larger than that of the reproducing head. In the conventional magnetic head constructed as shown in FIG. 23, the difference of height produced on the reproducing head side by the terminals 2 and 2 is reflected in the record gap 18. As a result, the gap of the recording head which has adopted a large track width suffers poor linearity and inevitably entrains an azimuth loss during the reading. The obscure track width of the magnetic reproducing head, therefore, causes azimuth loss.